Reduced circuit area is an economic driver of the microelectronics revolution. Integrated circuits, or chips, continue to increase in circuit density due to reduced sizes of circuit components made possible through the implementation of smaller and smaller circuit design rules. As more and more components are designed into an integrated circuit, the complexity of the integrated circuit is increased, thereby enabling greater functionality in the circuit. Moreover, functions that were once performed by multiple integrated circuits can often be integrated together onto the same integrated circuit, thereby reducing costs, power consumption, and size, while improving speed and interconnectivity.
In addition, other components such as capacitors, inductors, resistors, and other types of passive components are increasingly integrated into integrated circuits, thereby eliminating the need to incorporate separate, discrete components in a circuit design that otherwise increase circuit size, power consumption and cost. Both the demands of smaller circuit design rules, and the desire to incorporate various passive circuit components in an integrated circuit, however, has demanded new materials, new structures and new processing techniques to be incorporated into the integrated circuit fabrication process.
One type of passive component that is increasingly incorporated into many integrated circuit designs is a metal-insulator-metal (MIM) capacitor, which typically incorporates a stacked arrangement of materials that includes, in the least, top and bottom conductive electrodes incorporating a conductive material, and an intermediate insulator layer incorporating a dielectric material. Typically, a MIM capacitor is fabricated between the outermost metal layers in an integrated circuit (e.g., between the M5 and M6 layers), which orients the capacitor relatively far from the underlying semiconductor substrate, such that parasitic capacitance effects with the substrate are minimized.
MIM capacitors are often utilized, for example, in high frequency (e.g., RF) telecommunications applications such as in cell phones and other wireless devices, as well as other telecommunications products. Often, MIM capacitors are used to provide various functions in an integrated circuit, e.g., decoupling with a power supply, analog functions such as analog-to-digital conversions and filtering, and termination of transmission lines. Decoupling applications generally have relatively loose leakage current requirements, whereas analog applications, such as analog-to-digital converters (ADC's), typically require closer capacitor matching and relatively good voltage linearity. Moreover, in many telecommunications applications, particularly in handheld applications, low loss and relatively small temperature linearity are desired.
Given the ever-present desire to reduce the sizes of components in an integrated circuit, it is desirable to minimize the circuit area occupied by MIM capacitors. To provide a desired capacitance from a MIM capacitor within a smaller circuit area, therefore, an increase in the capacitance density of the capacitor (which based upon present design rules is typically expressed in terms of femtofarads per square micrometer (fF/μm2)) is required.
Conventional approaches to increasing MIM capacitor capacitance density have typically focused upon using high dielectric constant (K) dielectric materials in the insulator layer of a MIM capacitor, decreasing insulator layer thickness and/or utilizing structure geometries that increase perimeter (which increases fringe and lateral capacitance effects).
For example, high dielectric constant materials such as tantalum pentoxide, tantalum oxynitride, silicon nitride, barium strontium titanate (BST), lead zirconium titanate, and hafnium oxide have been used in some conventional MIM capacitor designs. Furthermore, various process improvements have been utilized to deposit such materials with reduced thicknesses, and without inducing short circuits between the electrodes of the capacitor design.
In addition, some MIM capacitor designs have relied upon multiple “fingers” forming one of the electrodes of a design. The multiple fingers extend generally parallel one another and incorporate an increased perimeter compared to a single contiguous electrode occupying the same circuit area.
Nonetheless, despite the improvements made in conventional MIM capacitor designs, many such designs are limited to at most about 1 fF/μm2. At this density, however, capacitors providing the necessary capacitance for many applications (e.g., many RF applications) are inordinately large, particularly for more advanced design rules. As an example, at 1 fF/μm2, a 100 nF capacitor would require a circuit area of approximately 1 cm per side, which, when used in connection with technology such as a 0.25 μm RF BiCMOS technology, results in a width that is approximately 40,000 times the minimum feature size for the integrated circuit.
Therefore, a significant need continues to exist in the art for a manner of improving the capacitance density in a MIM capacitor structure.
Another difficulty experienced in connection with MIM capacitor fabrication is oxidation of the bottom electrode during fabrication. Particularly when electrode materials such as titanium nitride (TiN) are used, oxidation of the electrode prior to deposition of the insulator layer can occur and form titanium oxides that cause current leakage. Prior attempts to inhibit oxidation include, for example, depositing the insulator layer in the same tool in which the electrode material is deposited. However, by depositing both layers in the same tool, patterning and etching of both layers must generally occur together, requiring the insulator layer to have the same layout as the bottom electrode. Furthermore, close coupling of the bottom electrode and dielectric film depositions does not guarantee a clean interface between the materials.
Therefore, a significant need also exists in the art for a manner of inhibiting the formation of oxidation on a bottom electrode of a MIM capacitor structure.
Yet another difficulty experienced in connection with MIM capacitor fabrication is that of patterning and etching the MIM capacitor structure in connection with aluminum-based circuit interconnects. In particular, whenever aluminum or aluminum alloy interconnects, as are commonly used in the metal layers of an integrated circuit, are exposed to etching chemistry such as CCl4, BCl3, Cl2, etc., aluminum chloride is often generated as a byproduct thereof, necessitating the use of an additional aluminum polymer removal step to clean the partially-fabricated integrated circuit. Adding such a step increases processing time and expense, and may not remove all chlorine (Cl) containing compounds that can cause Al corrosion.
Therefore, a significant need also exists in the art for a manner of etching a MIM capacitor structure without undue exposure of aluminum interconnects to chlorine chemistry.